1. Field of the Invention
This invention relates to a driver for use with a horn radiator to form a loudspeaker, more particularly to a driver which is capable of dissipating heat in an effective manner to prevent overheating in order not to adversely affect the performance of the driver.
2. Description of the Related Art
FIG. 1 illustrates a conventional driver 1 for use with a horn radiator 50 to form a loudspeaker. The driver 1 includes an annular coupling member 11 for coupling with the horn radiator 50, a yoke 12 secured to the coupling member 11, a permanent magnet 22 disposed inside the yoke 12, a flux guiding plate 23 superimposed on the permanent magnet 22, a washer 24 disposed on the yoke 12 around the flux guiding plate 23 and forming a gap 241 with the flux guiding plate 23, a diaphragm 25 having a top portion 251 spread above the flux guiding plate 23 and an annular extension 253 extending downwardly from the top portion 251 into the gap 241, a voice coil 252 disposed in the gap 241 and wound around the annular extension 253 of the diaphragm 25, and an acoustic phase equalizer 26 disposed above the diaphragm 25 and secured to the coupling member 11. When an electric signal is transmitted to the voice coil 252, the diaphragm 25 vibrates to result in compression of air, thereby enabling the horn radiator 50 to generate a sound output. When the permanent magnet 22 is an Al-Ni-Co magnet or a ferrite magnet, it usually has a relatively large size in order to provide a magnetic field with a sufficient strength. Accordingly, the yoke 12 for receiving the permanent magnet 22 has a relatively large size, and thus, a relatively large space 13 is formed between the yoke 12 and the permanent magnet 22. Heat that is generated by the voice coil 252 during the operation of the driver 1 can be effectively dissipated via the large space 13 and the yoke 12. However, when a smaller-sized rare earth magnet is used instead of the permanent magnet 22 to reduce the size of the driver, the space between the rare earth magnet and the yoke becomes much smaller. Heat dissipation becomes less efficient as compared to that when the larger-sized magnet 22 is in use. In view of the fact that the rare earth magnet is generally very sensitive to temperature and that the magnetic field of the rare earth magnet weakens significantly as the surrounding temperature rises, it is particularly important to provide the driver with a heat dissipating capability in order to prevent overheating and prevent an adverse affect on the performance of the driver.